High-temperature pebble-bed nuclear-reactor cores are generally received in a reflective housing or vessel which may be composed of cast material, such as graphite, provided with a top reflector which can be suspended from a support structure above the reactor core. The top reflector may also be composed of cast material, i.e. graphite and, in the event the cooling of the reactor core should fail for a prolonged period, it is possible for the suspension to give way, thereby allowing the top reflector to collapse.
It has been proposed to avoid this problem by forming the top reflector as a dome. However, this has been found to be disadvantageous because of its effect upon the operation and installation of other elements of the nuclear reactor, e.g. absorber rods which are frequently inserted through the cover or otherwise must be mounted in relation thereto. In addition, a domed configuration increases the cost and places structural units of the dome under stress, thereby increasing the forces which the cover structure must withstand.